1. Field of the Invention
The present invention relates to a signal recording apparatus for recording signals, such as video information, on tracks on a recording medium like an optical disk, and, more particularly, to an information signal recording apparatus for recording signals such as a video signal or audio signal whose reproduction speed is determined previously, on a writable recording medium which utilizes a change in pigment or a change in magnetism.
2. Description of Background Information
A WORM type (or direct read after write type) disk, which utilizes pigment, and a magnetooptic disk, which uses the magnetooptic effect, are known as writable recording media. In recording, for example, an audio signal on such a disk, the supplied analog audio signal is converted to binary values, redundancy for error correction is added to the binary signal, then the resultant signal is recorded in real time on the disk at a speed corresponding to the supplied audio signal.
The recording system would differ depending on the type of a recording medium of a disk in use. For example, when an organic pigment is used as a medium, for a signal of "1", intense light is irradiated on the disk to change the reflectance and the shape of the pigment. When the signal is "0", the disk will not be exposed to the light that causes such a change. Accordingly, the signal converted to binary values can be recorded on the disk. Any information once written on this type of medium cannot be erased.
With a magnetooptic type disk in use, intense light is given to the disk to increase its temperature to or above the Curie point, and, at the time of reproduction, the polarization status of reflected light is checked to find the signal level, thus ensuring recording and reproduction of binary signals. This method allows written information to be rewritten.
To check if information has been written correctly in such a real-time recording system, it is necessary to provide a separate pickup device for data reading and to trace recorded tracks with this pickup to verify the recorded signals.
If a write error is detected through the verification, it is necessary to record the position of the occurrence of the error on a specific portion on the disk, temporarily stop supplying the input signal and retry the recording for the erred signal (error correction). Reproduction of the recorded information data at the error-occurred portion should be made invalid and the subsequent data should be used instead. This requires that all the data be temporarily read into a computer or the like for reproduction, losing the real time performance, and that the reproducing apparatus should be equipped with a storage device of a large-capacity.
When pre-erasing of data from an erasable disk, such as a magnetooptic disk is needed, there also arises a problem that the real time performance will be lost.
One solution to the above shortcoming of magnetooptic disks was proposed in Japanese Patent Kokoku No. H3-13653.
According to the proposed method, the relative speed of a magnetooptic disk and the pickup at the recording time is set twice that of the reproduction to compress information along the time axis, so that erasure would be executed previously in real time.
Even with the use of this method, however, if a scratch, a defective portion or the like exists on the recording medium and writing has not been done properly, the aforementioned verification process should be performed at the expense of the real time performance in order to make the correction.
With the use of a WORM type optical disk that uses an organic pigment, in particular, if the disk contains a defective portion, it is not possible to continuously reproduce a spiral track to correctly read the recorded information. Even a slight defect on a disk would prevent the use of the whole disk. It is therefore necessary to carefully check stain or scratch on a WORM type optical disk, thus decreasing significantly the operability.